Thermo-resistive glide test head for disc drive recording media

Details Thermo-resistive glide test head for disc drive recording media Thermo-resistive glide test head for disc drive recording media

1997-05-13

2001-07-17

Strecker, Gerard R. (Department: 2862)

Electricity: measuring and testing

Magnetic

Magnetic information storage element testing

C073S010000, C360S025000, C374S007000

Reexamination Certificate

active

06262572

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to the field of disc drive data storage devices or disc drives, and more particularly, but not by way of limitation, to an improved glide test head, a topographic mapping head and improved systems for testing and characterizing the surface of disc drive recording media.
Disc drives of the type known as “Winchester” disc drives or hard disc drives are well known in the industry. Such disc drives record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 10,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent to the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator housing opposite to the coil, the actuator housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator housing rotates, the heads are moved radially across the data tracks along an arcuate path.
As the physical size of disc drives has decreased historically, the physical size of many of the disc drive components has also decreased to accommodate this size reduction. Similarly, the density of the data recorded on the magnetic media has been greatly increased. In order to accomplish this increase in data density, significant improvements in both the recording heads and recording media have been made.
For instance, the first rigid disc drives used in personal computers had a data capacity of only 10 megabytes, and were in the format commonly referred to in the industry as the “full height, 5¼ ″ format. Disc drives of the current generation typically have a data capacity of over a gigabyte (and frequently several gigabytes) in a 3½ ″ package which is only one fourth the size of the full height, 5¼ ″ format or less. Even smaller standard physical disc drive package formats, such as 2½ ″ and 1.8″, have been established. In order for these smaller envelope standards to gain market acceptance, even greater recording densities must be achieved.
The recording heads used in disc drives have evolved from monolithic inductive heads to composite inductive heads (without and with metal-in-gap technology) to thin-film heads fabricated using semi-conductor deposition techniques to the current generation of thin-film heads incorporating inductive write and magneto-resistive (MR) read elements. This technology path was necessitated by the need to continuously reduce the size of the gap in the head used to record and recover data, since such a gap size reduction was needed to reduce the size of the individual bit domain and allow greater recording density.
Since the reduction in gap size also meant that the head had to be closer to the recording medium, the quest for increased data density also lead to a parallel evolution in the technology of the recording medium. The earliest Winchester disc drives included discs coated with “particulate” recording layers. That is, small particles of ferrous oxide were suspended in a non-magnetic adhesive and applied to the disc substrate. With such discs, the size of the magnetic domain required to record a flux transition was clearly limited by the average size of the oxide particles and how closely these oxide particles were spaced within the adhesive matrix. The smoothness and flatness of the disc surface was also similarly limited. However, since the size of contemporary head gaps allowed data recording and retrieval with a head flying height of twelve microinches (0.000012 inches) or greater, the surface characteristics of the discs were adequate for the times.
Disc drives of the current generation incorporate heads that fly at nominal heights of only about 2.0 &mgr;″, and products currently under development will reduce this flying height to 1.5 &mgr;″ or less. Obviously, with nominal flying heights in this range, the surface characteristics of the disc medium must be much more closely controlled than was the case only a short time ago.
With the incorporation of MR heads in disc drives, a new type of media defect called a thermal asperity, or TA, has become of concern to the industry. Such defects are referred to as “thermal” asperities because they cause non-data related temperature variations in the MR element. These temperature variations result in resistance changes in the MR element, which in turn lead to read errors in the disc drive. Thermal asperities can be experienced in several modes, which will be discussed below.
The first mode in which TAs are exhibited can be referred to as “contact TAs”. Contact TAs occur when actual physical contact occurs between the MR element of the MR head and a “high” spot on the disc surface. Such physical contact causes rapid frictionally-induced heating of the MR element, with an attendant large rapid change in the resistance of the MR element. A simplified representation of the component relationship that causes a contact TA, along with the resultant effect on the read data channel, are shown in
FIGS. 11A and 11B
, respectively.
FIG. 11A
shows a head slider
130
which includes a MR read element
132
. This MR read element is sometimes referred to as a “MR stripe”. The nominal surface of a disc is shown at
134
, and the space
136
between the lower surface of the slider
130
and the nominal disc surface
134
represents the flying height of the slider
130
. The relative sizes shown for the slider
130
, MR stripe
132
and flying height
136
are not to scale and are for purposes of discussion only.
In the figure, the disc is moving relative to the slider
130
in the direction shown by arrow
138
.
As the disc rotates beneath the slider
130
, a high spot
140
on the disc surface passes under the MR element
132
. The vertical height of the high spot
140
is large enough that contact occurs between the disc and the MR element
132
. This contact causes frictionally-induced heating of the MR element
132
. As is well known in the art, such heating of the MR element
132
results in a proportional increase in the resistance of the MR element local to the point of contact. The effect

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